●Research Trends and Results

Analysis of conditions for growth of vegetation inestuaries and application of the results
AMANO Kunihiko (Phd(Eng)), HeadONUMA Katsuhiro, Senior Researcher
ENDO Maremi, Researcher
Environment Department, River Environment Division(Key words)estuaries, vegetation, ground level, tides, average submersion depth

2. Relationship between vegetation, ground level,
and average submersion depth
We have investigated the Natori River, Ibi River,
Yodo River, Ota River (Ota River Floodway) Yoshino
River, and Chikugo River, all with differingcharacteristic such as the scale of their tides. Based on
the results of topographical surveys (grid point
surveying at 50m intervals and vegetation boundaryline surveying) and vegetation surveys carried out by
various local management offices in 2009, elevationand vegetation data were organized in 10m meshes byinterpolation using GIS to analyze their mutualinterrelationships. We have normalized the elevation
using the equation defined below.

Reference document 1) shows the results of ananalysis for each community in each river. We defined
the mean submersion depth as the value obtained by
dividing the total depth of submersions through theyear at each ground level by the submersion time(∫(water level – ground level)dt/submerged time) ,analyzed the relation between the ground level relative
to tidal oscillation and the mean submersion depth ineach district surveyed, and plotted the ground levels at
which the reed communities begin to grow and atwhich their area of growth was largest (peak) in thefigure. (In case of the Natori River, the peak is notclear, so it is not plotted.). Although there is someNatoriRiverYoshinoRiverGround level relative to tidal oscillation

1. Introduction
In riverine estuaries, halophytes, reeds and othervegetation which are characteristic of such areas growthickly, contributing to the formation of the ecosystem.
Clarifying conditions for the growth of these types ofvegetation will contribute to appropriate rivermanagement which considers the environment ofriverine estuaries.
This report introduces the results of researchintended to generalize preferences in reeds andhalophyte communities.

Ibi River

Yodo River

Ota River

ChikugoRiverPeak

Growth begins
Synodic meanhigh tide
Ground level
relative to tidal
oscillationSynodic mean
low tide

Waterlevel
Mean submersion
depth

Mean submersion depth (cm)Figure Relationship of the Ground Levels where Reed
Communities begin to Grow and where they Peak withthe Mean Submersion Depth
scattering, excluding the Chikugo River where thetides oscillate greatly, growth began at mean
submersion depth of 40 to 70cm, and the vegetation
growth area peaked at between 15 and 30cm.
3. Utilization of the results
In the Ota River, the Chugoku Regional
Development Bureau constructed experimental tidal
flats for restoration with three types of cross section
shapes (completed in March 2010). At that time, it
was designed based on the results of a survey of theground level etc. of halophytes growing thickly in theupstream part of the test area, and the area of growthof Artemisia fukudo and other halophilous plants aregradually expanding. As the above shows, theprogress of the research on conditions for the growthof vegetation can contribute to the appropriate river
improvement
and construction of tidal flats
considering the environment.
[Reference]
1) Onuma, Endo, Amano, Kishida: Distribution ofvegetation and analysis of its relationship with thetide level on shorelines of brackish water areas in●Research Trends and Results
rivers, Collected Reports on HydraulicEngineering, Vol. 55, 2011.
2) Onuma, Fujita, Mochizuki, Amano: Research on
the framework of river mouth tidal flat design andmanagement methods taking the discharge
channel on the Ota River as an example,
Collected Reports on River Technology, Volume17, 2011.